Behind blacked-out windows and closed curtains, racecourses have found a new way to plug the holes left by the collapsed corporate hospitality market. In exchange for a fee, which can be impressively large in some cases, many tracks now hire out rooms to in-running gamblers seeking an edge over those betting from home.

"Everybody's at it on course," one professional in-running punter said this week. "The on-course bookmakers, the guys with ear-pieces who are on the phones to their mates back home, the press, punters with hi-spec mobile phones that can run off 3G and Wi-fi connections. There are more and more of them at every meeting. Everyone's trying to make a few quid."

Betfair, the online betting exchange, has allowed betting to continue during every British race since 2001. It estimates that in-running bets account for 20% of its trading volume on the average race.

Now racecourses hope to profit from in-running betting. Corporate hospitality boxes at tracks up and down the country are often full of groups of men in their 30s and 40s, each with his own laptop or computer terminal, using either the naked eye or the faster, unencoded pictures available at racecourses to make a profit.

By now most punters must be aware that they are at a vital disadvantage if they bet during a race while relying on pictures brought to them by cable or satellite, on the Racing UK or At The Races channels. In the case of At The Races, the pictures may be six or seven seconds behind the live action witnessed by those at the track.

Those who are not aware of the disparity presumably find out quickly enough through harsh experience, even though having the fastest pictures is no certain route to success.

At Lingfield last Tuesday two boxes were occupied by in-running punters while an entire suite at the rear of the building had been hired on a long-term basis by an enterprise which sub-let 'workstations' to punters by the day.

"I usually have a couple of boxes ofin-running guys," one course manager said. "They are model customers. They don't want anything more than tea and coffee and a plate of biscuits. They arrive just before the first, they leave straight after the last and they don't make a mess.

"I was approached by a guy who wanted to hire a box with wi-fi for the whole year. There would be some of our bigger days when I would have no problem getting a good price for that box but others when I would be struggling to fill it. I quoted a price for the year which covered the loss of revenue on our premium days and he said yes straight away.

"I can't see what the problem is. These aren't punters; they're professionals who don't want to bet in cash at the track. The money they are putting into the racecourse can be used to invest in other areas."

At Leicester the former Tote Credit office adjacent to the parade ring behind the grandstand has been converted into an in-running facility which, despite having been in operation for only a few months, now attracts 20 or more individual players to each meeting.

Last Monday there were two boxes occupied with in-running punters at Plumpton. One frowned and drew the curtains when he saw he was being obs-erved from the grandstand. At Kempton on Sunday, one box was occupied by "a regular in-running punter".

Courses who permit in-running punters to operate in this way risk alienating several groups. On-course bookmakers, who have paid for their pitch, may see it as undermining their business, while off-course firms, some of which sponsor races at these tracks, may also take umbrage.

Casual punters may be angered that racecourses are assisting those who seek to tilt the odds in their favour, but the legal position is unclear. A spokesman for the Gambling Commisssion said: "Consumers using exchanges or bookmakers are not prevented by the Gambling Act from using a mobile phone or internet connection to bet in-running from racecourses."

But Nic Coward, chief executive of the British Horseracing Authority, takes a different view. "This sounds like the kind of evidence of exchange customers acting in the course of a business, on an unlicensed basis, that the DCMS are very interested in," he said last night.

"Anyone doing this would fall under the Levy Act's definition of a bookmaker and should therefore be paying levy. The Gambling Commission would no doubt want to take a serious look at this."